Red ground cover under tomatoes

Margaret6a(6a IN)March 18, 2006

Anyone have advise on the success of using red plastic under tomato plants? I know some tests have been done in some universities that say it will boost your harvest by 20%. However, when looking on the tomato forum, I did not find that anyone felt this was particularly advantageous. What's your take on this?

I can't think of a single reason why red plastic would work any better than any other color plastic. I presume the plastic helps to keep the soil warmer and more moist. But I really I can't imagine what the color red adds to the method. Maybe the red attracts hummers and other polinators better than other colors. Or maybe it makes the little yellow flowers stand out better.

How many people did you find at the tomato forum that had actually tried it? If the answer is none, then that's a pretty good reason to give it a whirl yourself if it interests you.

I think the theory is that red reflects the part of the light spectrum that helps the plants grow while still warming the soil.

I tried it several years ago, but didn't notice enough of a difference to justify the additional cost. But I didn't do a controlled experiment with some on red plastic and some on black. The variation in weather from one year to the next could more than account for extra productivity.

Why not try your own experiment? Some with red plastic, some the way you usually grow? Then you'll know what works for you and can let the rest of us know.

The jury is still out. I ignore commercial opinions, like people who manufacture or sell the stuff, and concentrate on university trials. Here's a sample:

Cornell on Red Mulch:

"There has been much discussion recently about using specific colored mulches on different vegetable crops to achieve earlier or higher yields. When used by a roadside stand, these mulches can certainly draw quite a bit of attention! However, the research results from studies examining red mulch under tomatoes is very conflicting- in some cases, a yield benefit was observed, in others, no benefit. Different tomato varieties also appear to respond differently to the red mulch. The scientific theory behind using red mulch is sound- a specific pigment system in plants (phytochrome) responds to specific red wavelengths of light. If we enhance those wavelengths in the plant canopy, we should be able to change plant growth. The effect of red mulch, like that of IRT (Infra-red Transmitting) mulches, depends on sunlight levels. Part of the variation in results in the Northeast may be related to the differing levels of total sunlight and average air temperatures.

Red mulch can act like an IRT much and will increase soil temperatures compared to black mulch. Some of the benefit to tomatoes is suspected to be due to this temperature effect. If used for the early plantings, some yield benefit may be observed with red mulch due to soil warming. When used with main season plantings, the effects of red mulch may be more variable. Red mulch, however, is more expense than IRT, requiring careful consideration of crops and markets you are targeting. Start small if you are considering experimenting with these colored mulches. There have been problems with both the product quality (breaks down early, may need more UV stabilization, prone to tearing) and visible light transmission (poor weed control under many of these). Research continues on the use of red and other colored mulches around the region, and hopefully, we will soon have some field scale trials and economic analysis of these products. "

Montana State University:

"I headed a study that for two years examined the uses of colored plastic mulches on tomatoes and peppers, two high-priced crops that are sometimes difficult to ripen sufficiently in areas with cool summer nights and short growing seasons. Here's what we did, and here's what we found out.

We planted tomatoes and peppers in the 1999 and 2000 seasons at Bozeman. Some we maintained in bare plots and some we kept mulched with either red, silver, or black plastic. Let's talk about peppers first. In 1999 the various treatments had no effect upon the total number of fruit each plant bore, though in 2000, plants mulched with either silver or red mulch bore more fruit than plants in the other treatments. In 1999, plants mulched with red and silver plastic set more fruit earlier than those on the other treatments. In 2000, plants on red mulch had the greatest early fruit set. In both years, plants mulched with either red or silver plastic set more fruit earlier than those on the other treatments. So it looks like red and silver plastic mulch speeds up fruit ripening in sweet peppers. Silver plastic mulch also significantly increases the number of roots in sweet pepper plants, potentially allowing them to grow bigger and produce more fruit.

We also grew tomato plants on bare soil or in plots mulched with either silver, red, or the traditional black plastic mulches. In 1999, plants grown on silver or red mulches produced the greatest number of fruit, while in 2000, those grown on silver mulch produced the greatest number. On the other hand, plants in both years grown on silver and red mulches produced the greatest early fruit set and the greatest number of ripe fruit.

To make sense of all this, red and silver plastic mulches produced the greatest number of ripe fruit and early set of any of the treatments. This is important in colder areas of our region where hot summer days are followed by cool nights and where the entire growing season is marginal for these crops. And the experiments are important in showing that black plastic mulch may not be the best one to use. In fact, in our study, black plastic was fairly comparable to no mulch at all regarding fruit set and ripening.

Now, as with all research, this experiment must be repeated in many areas of our region over many years in order for us to flesh out the entire effect of colored plastic mulches on crop production. But we can now say, at least, that silver and red mulches speed ripening in tomatoes and peppers under Bozeman conditions. Do your own studies. Try red and silver plastic mulches in your garden on these and other crops and let me know what happens. "

University of Vermont:

"Studies of red mulch have not shown consistent results. Red mulch sometimes increases yield of tomatoes, but not always. Different tomato varieties also appear to respond differently to the red mulch. The effect of red mulch, like that of IRT, depends on sunlight levels, so the variation results in studies may be due to different light conditions, as well as different temperature conditions. Red mulch does tend to increase soil temperatures much like an IRT, so in early plantings it is likely to promote earlier yields. When used with main season plantings, the effects of red mulch may be more variable."

UCONN (& Penn State)

"Red mulches were the first really new color to be investigated, other than the ones mentioned above and have started to be used commercially. There have been alot of trials on tomatoes, some that have shown a benefit either of improved yields or enhanced ripening and quality of the fruit. In other trials, there has not been a response. There is also some indication from different trials that red mulch may also be reducing the severity of early blight on tomatoes. This is indeed an interesting finding that may have some real benefit. Red plastic mulch has also been shown to increase yields in zucchini and in honeydews and muskmelons. In a study in New Hampshire, researchers found that differences in reflectivity among a red, black and red on black mulch were minimal at 16 inches above the mulch surface and on the shaded side of the row. They speculate that for red mulch reflectivity to have a more sustained and more consistent effect on biomass accumulation and yield in tomato, the rows may need to be oriented in a North-South direction.

A summary of two years research at Penn State on crop response to red, brown IRT, green IRT, black, silver, white, blue (light and dark) and yellow color mulch is presented below:

Peppers. No significant difference in yield of marketable peppers fruit (cv. Enterprise) from clear, yellow, black, silver, red and brown IRT mulch. Fruit grown on yellow produced the smallest fruit. Silver, red and clear mulch appeared to hasten maturity of the peppers harvested compared to the black or yellow treatments. In 1998, plants grown on silver mulch significantly produced more marketable pepper (cv. Marengo) compared to those grown on white mulch. There were no significant differences in marketable pepper among the other colors (green and brown IRT, black, red, yellow and blue). Pepper plants grown on either silver or green IRT mulch produced larger fruit compared to brown IRT, black, red, white, yellow or blue mulches. Highest soil temperature, taken on August 3, 1998, was recorded under green IRT mulch 103 o F and coolest under white (89o F).

This light reflectivity can affect not only crop growth but also insect response to the plants grown on the mulch. Examples are yellow, red, and blue mulches, which increased green peach aphid populations, especially the yellow color, which attracted increased numbers of striped and spotted cucumber beetles. There may exist the potential to use this information in developing an insect management program where a row of yellow mulch is laid in the field after a certain number of rows of whatever mulch is being used for the crop. It would be considered a trap row. In a trial in Pennsylvania, the highest yield of peppers was from yellow mulch. Since, it has been proven that insects are attracted to this color, a grower has to really be on top of their scouting for insects. Yellow has long been used in greenhouses and now in high tunnels to monitor insects.

Similar to a white color mulch mentioned previously, the degree of opacity of these newer colored mulches may require a herbicide or fumigant to be used to prevent weed growth. Some of these colored mulches, for example blue and red, can have a dramatic impact on the soil temperatures, raising soil temperatures to 167o and 168o F, respectively, at the 2-inch depth when the ambient air temperature was 104 o F (my research in Kansas).

Summary. There are still many aspects of colors that we really do not understand. We know that we can build a mulch to specific spectral parameters or wavelengths and that will determine the color. The color of the mulch will influence the soil temperature, the surface temperature of the mulch and the light reflected by into the plant canopy. We know the blue color in the 440-495nm wavelength band will cause a plant response- phototropism, photosynthesis; while red color in the 625-800nm wavelength band will influence photosynthesis, seed germination, seedling/vegetative growth, and anthocyanin synthesis. Another impact on the effectiveness of a color is if the mulch is applied to a raised bed or is laid flat on the ground. This can cause a difference in the impact a mulch can have on the soil and plant microenvironment. The last consideration is the difference in color retention, film appearance, and film longevity of mulches currently on the market. This is the critical question of what really is a red, blue or yellow mulch and how best do we define it. To anyone who has ever look at a color additive chart, the problem is readily apparent. A lot more research still needs to be done on the effect different colors have on the microclimate, vegetable crop growth, yields and earliness."

Thanks for all your good advise. I may try it just for grins and giggles-like Donn, I find much of the fun is in the experimenting with different methods. Someone on the tomato forum suggested that the results are short-term because, once your plant gets large and bushy, there is little reflectivity. I plant mostly Big Boys and Better Boys because I get such good yields from them. The plants get quite large and bushy. This year I am also WSing the plants on the front of the Burpee catalog because they looked so great. I'd love to find a striped tomato that looks good on a serving tray but tastes good too. Tried a striped one two years ago that looked good but had absolutely no taste-Boo.